Assess your student's math level. The Home School Legal Defense Association and Texas Education Agency websites have downloadable tests and evaluations to assess your child's progress. Administer one or more math test in the last math grade your child has completed to diagnose trouble areas where you child needs remedial help.
Focus lessons in your child's problems areas. Because math concepts are sequential, back up to the foundation area of trouble spots.
Use the time that you spend teaching math to provide remedial teaching until your child masters the concepts he is having trouble understanding. Play games that involve math or spend additional time examining the material. As your remedial work helps to solve your child's issues, your child should be able to progress through math lessons.
Expect catching up to take time. Stay positive and work on helping your child learn the math fundamentals.
Consider hiring a tutor to provide additional help. Sometimes a different teacher can bring a different perspective to a difficult learning situation.